The human body utilizes the energy produced when breathed-in oxygen molecules (O2) are reduced to water with a food-derived reducing substance by mitochondria. During this process, some of the oxygen molecules are converted into active oxygen (O2−). Active oxygen is an unstable substance that tends to act as a starting material in the production of hydroxyl radicals (OH.), which tend to be stabilized by taking an electron from the DNA of the human body. Hydroxyl radicals harm DNA, cause arteriosclerosis, contribute to the occurrence of cancer, and are a large factor in lifestyle-related diseases.
Recently, Professor Shigeo Ohta from the Institute of Gerontology, Nippon Medical School, reported in Non-Patent Document 1 that hydrogen molecules decrease active oxygen in the human body. A research team from Nippon Medical School performed an experiment on rat neurons grown in a test tube and confirmed that a solution with a hydrogen concentration of 1.2 ppm reduces and detoxifies active oxygen. Since hydrogen easily infiltrates even the interior of the cell nucleus, genes can also be expected to be protected from attack by active oxygen.
Therefore, technologies for producing water in which hydrogen molecules are dissolved efficiently and at a low cost are being focused on. Methods for producing water in which hydrogen molecules are dissolved can be broadly divided into the following two types.
(1) Dissolving hydrogen gas in water under high pressure.
(2) Producing hydrogen molecules directly in water by cathode electrolysis using an electrolytic cell.
Although the hydrogen gas dissolution method of (1) is simple, a pressure vessel for hazardous substances is required, the method is not easy-to-use, and the method is expensive. In addition, since hydrogen gas is a hazardous substance, the use of a hydrogen gas cylinder in the home would be difficult.
The electrolysis method of (2) holds promise for apparatuses for cheaply producing in the home water in which hydrogen molecules are dissolved. Conventionally, an alkaline ion water generator has often been used as an electrolysis apparatus for use in the home. Originally, alkaline ion water generators were designed to produce weakly alkaline water having a pH of 7 to 8.5 by electrolyzing tap water and the like in order to combat gastric hyperacidity. This type of apparatus includes, as shown in FIG. 18, a two-chamber electrolysis apparatus that divides an anode chamber 1 having an anode electrode 4 and a cathode chamber 6 having a cathode electrode 9 into two chambers by a diaphragm 5. The water to be treated is supplied from an anode chamber inlet 2 and a cathode chamber inlet 7 and electrolyzed by the anode electrode 4 and the cathode electrode 9. The electrolyzed water is discharged from an anode chamber outlet 3 and a cathode chamber outlet 8. In this case, since the diaphragm 5 and the electrodes (anode electrode 4 and cathode electrode 9) are separated, in order for electricity to flow an electrolyte needs to be included in the water supplied to the electrolytic cell. However, tap water contains 100 to 200 ppm of alkali metal ions such as sodium ions, and anions such as chloride ions. Consequently, for tap water in which sodium and chlorine are dissolved, the following reactions are possible.
Reactions at the Anode Electrode2Cl−−2e−→Cl2  (1)2H2O−4e−→O2+4H+  (2)Reactions at the Cathode Electrode2Na++2e−→2Na  (3)2Na+2H2O→2Na++H2+2OH−  (4)2H2O+2e−→H2+2OH−  (5)
As can be seen from the above, alkaline water can be obtained in which hydrogen molecules are dissolved in cathode-electrolyzed water discharged from the cathode chamber 6. In order to use the produced electrolyzed water as drinking water, it is required under the Water Supply Act that the pH is 8.5 or less. When the two-chamber electrolytic cell illustrated in FIG. 18 is used, there is an increased chance that the pH will be 8.5 or more if strong electrolysis is carried out, so that the produced cathode-electrolyzed water will not be suitable as drinking water. Further, if the electrolysis current is reduced to try to lower the pH, the hydrogen molecule concentration will naturally decrease. Consequently, an effect from the hydrogen molecules cannot be expected. Thus, the conventional two-chamber electrolytic cell illustrated in FIG. 18 is not suited as a hydrogen-dissolved drinking water production apparatus.
One way to carry out strong electrolysis is to use pure water having a low conductivity. An example of an electrolytic cell for electrolyzing pure water having a low conductivity is the two-chamber electrolytic cell illustrated in FIG. 19 (constituent elements that are the same as those in FIG. 18 are denoted with the same reference numerals, and a description thereof is omitted here). In this case, the cathode electrode and the anode electrode are closely adhered to the diaphragm. To efficiently electrolyze the water, the cathode electrode and the anode electrode need to be formed like a net or punched metal, or be provided with many through holes so that water can permeate therethrough (hereinafter, this is referred to as “water-permeable”; in FIG. 19, the water-permeable anode electrode is represented by reference numeral 4-1, and the water-permeable cathode electrode is represented by reference numeral 9-1). In addition, using a fluorine-based cation exchange membrane as the diaphragm enables pure water to be electrolyzed at a low voltage (in FIG. 19, the diaphragm formed from a fluorine-based cation exchange membrane is represented by reference numeral 5-1). Since pure water is electrolyzed, basically there is no change in the pH of the cathode-electrolyzed water, so that the electrolysis current can be increased. Further, when electrolyzing ultrapure water having an alkali metal ion concentration of ppt or less, since basically no large change is seen in the pH of the cathode-electrolyzed water, the electrolysis current can be increased. However, in the case of a low-cost electrolysis apparatus for home use, tap water purity will probably be less than that of ultrapure water, and thus the alkali metal ion concentration would be expected to be several ppm.
The produced hydrogen molecule amount is proportional to the electrolysis current. When the cathode-electrolyzed water is provided as drinking water, how the hydrogen molecules are present in the water is important. To be suitably absorbed into the human body, the hydrogen molecules need to be dissolved in water. The produced hydrogen molecules can broadly be classified as hydrogen gas in the form of bubbles and dissolved hydrogen molecules. The hydrogen gas in the form of bubbles quickly evaporates into the air, which reduces the proportion that is absorbed into the human body. The dissolved hydrogen molecules are present in the water as single molecules, a plurality of molecules and the like. In such a state, the life of the dissolved hydrogen molecules increases, and the chances of absorption into the human body improve.
When electrodes having the same external dimensions are used, it can be thought that to increase the produced hydrogen concentration in the cathode-electrolyzed water, the hydrogen production amount needs to be increased by increasing the current density. However, it has been reported that the efficiency of the produced hydrogen molecules dissolving in the cathode-electrolyzed water depends on the current density and the flow rate on the electrode surface. It is known that dissolution efficiency decreases as current density increases. Therefore, an optimum current density exists. Moreover, it is known that the dissolution efficiency depends on the flow rate on the electrode surface, and that the dissolution efficiency is larger, the faster the flow rate is. However, because the amount of the cathode-electrolyzed water increases if the flow rate is increased, a larger dissolution efficiency does not always mean that the dissolved hydrogen molecule concentration will increase. More specifically, an optimum flow rate also exists.
Based on the above standpoint, when high-purity water such as pure water is used, a two-chamber electrolytic cell like that illustrated in FIG. 19, in which the anode electrode and the cathode electrode are closely adhered to the fluorine-based ion exchange membrane 5-1, is suitable. However, in this case, to dissolve the electrolysis product in the electrolyzed water, both the anode electrode and the cathode electrode need to be water-permeable, and closely adhered to the fluorine-based ion exchange membrane diaphragm. Using a water-permeable electrode means that the effective surface area is reduced, so that the effective current density is increased. This means that the optimum current for a water-permeable electrode is smaller than the optimum current for a cathode electrode having the same dimensions without holes. Further, since the water-permeable electrode needs to be closely adhered to the diaphragm, electrolysis occurs at the edge portions of the holes in the water-permeable electrode. Consequently, the effective surface area for electrolysis is further reduced. Thus, compared with an electrolytic cell having the same dimensions, the produced amount of dissolved hydrogen molecules for an electrolytic cell provided with a water-permeable electrode is reduced. Therefore, to reduce costs, a structure that uses an electrode having a small hole surface area and that has a small contact area with the diaphragm is preferred.    [Non-Patent Document 1] Nature Medicine Electronic Version 2007 May 8 (Published online: 7 May 2007; doi:10.1038/nm1577)